The invention relates to an electrode suitable for use in industrial electrochemical processes, for instance in electrolytic applications involving an oxygen evolution anodic reaction. Oxygen-evolving anodes are widely used in several electrochemical applications, many of which fall in the domain of electrometallurgy and cover a wide range in terms of applied current density, which can be very low (for instance few hundreds A/m2, as in electrowinning processes) but also very high (for instance fast plating, in which 10 kA/m2 referred to the anodic surface can be exceeded). Another field of application for oxygen-evolving anodes is given by impressed current cathodic protection. Electrodes suitable for anodic oxygen evolution can be obtained starting from valve metal substrates, for example titanium and alloys thereof, coated with catalytic compositions based on transition metals or alloys thereof, characterised by their capability to lower the oxygen discharge anodic overvoltage, too high to allow carrying out industrial processes in the absence of catalytic systems. A composition suitable for catalysing anodic oxygen evolution comprises, for instance, a mixture of oxides of iridium and tantalum, wherein iridium constitutes the catalytically active species and tantalum favours the formation of a compact coating, capable of protecting the valve metal substrate from corrosion phenomena especially when operating with aggressive electrolytes. An anode formulation suitable for anodic oxygen evolution in many industrial electrochemical processes comprises a titanium substrate and a catalytic coating comprising iridium and tantalum oxides of molar composition referred to the metals of 65% Ir and 35% Ta. In some cases, for examples to be able to operate with very acidic or otherwise aggressive electrolytes, it can be advantageous to interpose a protective interlayer between the titanium substrate and the catalytic coating, for instance comprising titanium and tantalum oxides of molar composition referred to the metals of 80% Ti and 20% Ta. This kind of electrode can be prepared in several ways, for example by thermal decomposition at high temperature, for instance from about 400° C. to about 600° C., of a precursor solution. An electrode with the above-specified composition can meet the needs of many industrial applications, both at low or high current density, with reasonable operative lifetimes. The economics of some productive processes especially in the metallurgical domain (for instance copper deposition in galvanic processes for the manufacturing of printed circuits and copper foil) nevertheless require that electrodes have a higher and higher duration, versus a suitably reduced oxygen evolution potential also at high current density. Oxygen evolution potential is one of the main factors in determining the process operative voltage and therefore the overall energy consumption. Moreover, the operative lifetime of anodes based on noble metals or oxides thereof on valve metal substrates is remarkably reduced in the presence of particularly aggressive pollutants, capable of establishing accelerated phenomena of corrosion or of fouling of the anode surface. An example of the former type is given by fluoride ions, which determine a specific attack on valve metals such as titanium deactivating the electrodes very quickly. In some industrial environments, remarkable costs have to be faced to reduce fluoride concentration to extremely low levels, since a fluoride ion content higher than 0.2 parts per million (ppm) can be capable of showing effects on the duration of the anodes. An example of the latter type is conversely given by manganese ions, present in several industrial electrolytes in a typical amount of 2-30 g/l, which starting from concentrations as low as 1 g/l have the tendency to film the anode surface with an MnO2 layer liable to blind their catalytic activity and being difficult to remove without causing damages.
It has been, therefore, made evident of the need to provide anodes for oxygen evolution characterised by higher operative lifetimes even in particularly critical process conditions, such as a high current density or the presence of particularly aggressive electrolytes, for instance due to the presence of contaminant species.